MATURE 
ing this most fascinating question, which I venture to put 
before the Royal Society. Although I cannot pretend to 
an intimate acquaintance with the more intricate pheno- 
mena of solar physics, I have long hada conviction 
derived principally from familiarity with some of the 
terrestrial effects of heat, that the prodigious and seemingly 
wanton dissipation of solar heat is unnecessary to satisfy 
accepted principles regarding the conservation of energy, 
but that it may be arrested and returned over and over 
again to the sun, in a manner somewhat analogous to the 
action of the heat recuperator in the regenerative gas 
furnace. The fundamental conditions are :— 
1. That aqueous vapour and carbon compounds are 
present in stellar or interplanetary space. 
2. That these gaseous compounds are capable of being 
dissociated by radiant solar energy while in a state of 
extreme attenuation. 
3. That these dissociated vapours are capable of being 
compressed into the solar photosphere by a process of 
interchange with an equal amount of reassociated vapours, 
this interchange being effected by the centrifugal action 
of the sun itself. 
If these conditions could be substantiated, we should 
gain the satisfaction that our solar system would no longer 
impress us with the idea of prodigious waste through 
dissipation of energy into space, but rather with that of 
well-ordered self-sustaining action, capable of perpetuating 
solar radiation to the remotest future. 
FURTHER OBSERVATIONS ON THE FRESH- 
WATER MEDUSA, MADE DURING THE 
SUMMER, 1881 
i. HE Freshwater Medusa—ZLimunocodium Sowerbii 
—reappeared in the lily-house tank in the Bo- 
tanical Gardens, Regent’s Park, during the summer of 
1851, as the readers of NATURE were duly informed. 
In spite of the renewed opportunities for study thus 
afforded, the life-history of this interesting organism still 
remains a mystery, and it is still exceedingly difficult to 
frame any hypothesis as to the original introduction of 
the jelly-fish into the tank where it was discovered by 
Mr. Sowerby in 1880. 
The only general hypothesis which can be entertained 
as to the original introduction of the jelly-fish, is that it 
came “in some way at some time” with plants deposited 
in the tank. 
It is tmprobadle that the jelly-fish can have existed for 
many seasons in the tank unobserved, though Jossib/e, 
supposing that it first appeared in small numbers. 
The last importation of an aquatic plant into the lily- 
house in Reyent’s Park, previous to the discovery of the 
jelly-fish in June, 1860, is that to which suspicion naturally 
attaches itself. This importation occurred early in March, 
1879, when, as Mr. Sowerby kindly informs me, a Miss 
Tupper, whose address is not in his possession, presented 
to the Royal Botanical Society a specimen of a species of 
Pontederia. This specimen was wrapped in a piece of 
brown paper, was about one foot long, was crushed and 
as dry as hay, in fact the Garden superintendent and the 
man in charge of the tank thought it dead. The speci- 
nen is believed to have come from Brazil. It vegetated 
after being placed in the tank, and has given rise to a 
copious growth, part of which is now in the lily-house of 
the Botanic Garden at Oxford. 
Mr. Sowerby cannot remember the introduction of any 
new plants into the tank at such time previous to this as 
would render it probable that the jelly-fish were introduced 
on such previous occasions, 
It is clear, then, that if the jelly-fish were introduced 
with the Pontederia, either the animal itself or its eggs 
must have great power of resistance to partial desiccation. 
Of this power of resistance we have no further evid- 
ence, for the tank in the Lily-house is not completely 
emptied and dried in the winter, though the water is run 
off, a deep trough of water and mud remains permanently 
at one end of the tank. 
At the same time it is in accordance with what is 
known as to many lacustrine animals that the eggs or 
young stages of the fresh-water jelly-fish should be able 
to resist partial desiccation. Hence the theory of its 
introduction with the Pontederia is, though far from de- 
monstrated, yet quite tenable. Plants of this Pontederia 
were sent from Regent’s Park to Kew and Oxford (where 
they are flourishing) some months before the discovery of 
the jelly-fish in June, 1880. But no jelly-fish made their 
appearance in consequence (so far as is known) in the 
tanks at Kew and Oxford. Hence the association with 
the Pontederia of the eggs or young of the jelly-fish can- 
not have been a very intimate one. 
2. The history of the jelly-fish in the Regent’s Park 
tank is as follows :—It was first seen by Mr. Sowerby on 
June 10, 1880. At that time there were some specimens 
nearly full-grown and a vast number of very young ones 
(apparently recently hatched) also. By the end of July 
not a specimen could be found in the tank. All the 
mature specimens examined by me in 1880 were males, 
numbering 150. I entirely failed to obtain any specimen 
which was female, either young or mature. Nevertheless 
Mr. Sowerby was of opinion that young were produced 
by adult individuals isolated and kept by him in a small 
glass jar. These young were those which I reported on 
in the Quart. Fourn. Micr. Sci., January, 1881. I could 
find only adult males in the jar with them, and think that 
it is possible (though not certain))that the young were 
hatched from eggs floating in the water when first intro- 
duced into the jar. They would thus be only /aée- 
hatching members of the same brood of which adults were 
discovered on June 10. It is, on the other hand, possible 
that they belonged to a second generation. 
The males observed in 1880 discharged abundant 
motile spermatozoa from their genital sacs and were 
obviously ready for procreation. 
Thus in 1880 we were left in ignorance of the female 
of Zimnocodium, and in nearly complete ignorance as to 
the period and mode of reproduction. 
3. In 1881 Mr. Sowerby observed the Medusa again, 
only two days after the anniversary of their first appear- 
ance, namely, on June 16. He states, in a Jetter kindly 
written for me, that only a “few were seen, although the 
water appeared swarming with minute individuals just 
large enough to be distinctly seen with the naked eye. 
Many of these we determined by examination with a 
glass; they did not, however, appear to come to man- 
hood, and about the 25th of June the whole of the 
Medusz vanished.”’ 
It is obvious that some process of reproduction had 
taken place between June, 1880, and June, 1881, giving 
rise to the Medusz observed in 1881. Where wer: 
the females which produced the eggs from which this 
new generation was born? As in 1880, so in 1881, 
when first observed in June, doth minute young apparently 
Just hatched, and also full-grown tndividuals were simul- 
tancously detected. In 1881 I examined about fifty of the 
full-grown individuals from the Regent’s Park : as in 1880 
they were all males. It seems probable that the adults 
observed on June 10 were merely early-hatched members 
of the same brood as the young (of various ages and 
sizes) which abounded with them. 
From the experience of these two years it appears pro- 
bable that the first specimens which hatch out must do so 
six weeks or two months before the middle of June. But 
as to the character of the eggs from which they hatch, 
we have as yet no idea. It would seem likely that 
those eggs were deposited before the emptying of the 
tank in December, and probably enough in the sum- 
mer before the dying down of the males, so abun- 
dant until their total disappearance at the end of July. 
